Modern wireless communication devices typically include a baseband section, an RF transmitter section and an RF receiver section. In broad terms, when the wireless device operates in transmit mode, the baseband section processes signals before they are modulated and up-converted for transmission by the RF transmitter section at a higher frequency than employed in the baseband section. When the wireless device operates in receive mode, the baseband section processes signals after they have been down-converted by the RF receiver section. The transmitter section and receiver section together form an RF transceiver section. The baseband section and the RF transceiver section may be fabricated on the same integrated circuit (IC) or alternatively on separate integrated circuits that are interfaced with one another. The RF transceiver section includes a frequency synthesizer that controls the transmit and receive frequencies of the communication device.
Both the RF transmitter section and the RF receiver section may employ a digital signal processor (DSP) to facilitate a number of signal processing tasks. For example, the transmitter section may employ the DSP to perform voice encoding, channel encoding and frequency burst generation tasks. The receiver section may employ the DSP to perform equalization, channel decoding and voice decoding tasks. As miniaturization continues forward, the components of a wireless communication device come closer and closer together. Unfortunately, with such advances in miniaturization, it is possible that noise generated by the digital activities of the DSP may couple to the receiver section of the device and hinder RF signal reception.
Time domain isolation provides a way to effectively silence noisy digital circuits such as the DSP during time periods when the receiver section is active. In broad terms, time domain isolation provides that noisy components such as the DSP are disabled at times when the RF receiver section is conducting noise sensitive signal receiving activities. In this approach, time is divided into alternating RF time slots and signal processing time slots. The RF receiver section is enabled during RF time slots and disabled during signal processing time slots when the DSP is active. The DSP is enabled or active during the signal processing time slots and disabled or inactive during the RF time slots when the RF receiver section is active.
In one time domain isolation implementation, an audio codec in a digital to analog conversion (DAC) path receives signal samples from the DSP and coverts them into an analog audio output signal. The DAC path includes one or more buffers that store received samples that were received when the RF receiver section was enabled. These buffers are used to help prevent audio underflow when the RF receiver section is disabled and the DSP is enabled. Audio underflow occurs when insufficient data is received from the DSP by the audio codec that converts the received samples or data to an analog audio output signal. If audio underflow occurs, it may be heard as an annoying gap or pop in the audio output signal of the audio codec. While buffers are helpful in reducing audio underflow in wireless communication devices using time domain isolation, audio underflow may still occur under some circumstances.
What is needed is a wireless communication device that further reduces the likelihood of audio underflow in the wireless communication device.